Until the early 1950's, commonly used pressure-sensitive adhesives ("PSAs") for skin applications were based on natural or synthetic rubber compositions compounded with low molecular weight tackifiers, plasticizers, stabilizers, etc. These adhesives had the disadvantage of being hydrophobic and incapable of absorbing water. Thus, such adhesives would trap water under the covered area, often causing skin maceration or other skin damage. Furthermore, the low molecular weight ingredients compounded into these adhesives often would penetrate the skin, causing irritation or sensitization.
Polyacrylate PSAs are an improvement over the rubber-based adhesives, partly due to their self-adhesive property. This property allows them to be prepared as single-component polymeric materials without the need for potentially allergenic modifying or tackifying agents. However, these adhesives often contain unreacted residual acrylic monomer as an impurity in an amount which would irritate and/or sensitize skin. Although these polyacrylate PSAs are much more permeable to moisture or water vapor than are the rubber-based adhesives, they are incapable of absorbing any significant amounts of moisture or water. Therefore, when used for long duration in skin or wound care applications, adhesion is compromised and/or skin damage or maceration may result.
One variation of these polyacrylate PSAs is disclosed in U.S. Pat. No. 4,914,173 to Ansell. The specific PSAs of that patent are obtained by reacting an isocyanate prepolymer, which is the reaction product of a poly-functional isocyanate and a polyoxyalkylene diol monoalkyl ether, with a hydroxy-containing ester of acrylic or methacrylic acid to form a functionalized prepolymer and then cross-linking the polymer by irradiation to form a PSA that is not self-adherent but is capable of absorbing up to 95% by weight of water when hydrated. Although useful in applications where the adhesive will contact a moist or wet environment, these adhesives do not have sufficient tack or initial adhesive properties to be adherent to the skin for certain uses.
An advance in PSA formulation for skin and particularly for wound care applications was the development of compositions comprising blends of one or more water-soluble or swellable hydrocolloids and a tacky, viscous, polymeric material such as polyisobutylene as disclosed in Chen U.S. Pat. No. 3,339,546. Another example is Doyle et al. U.S. Pat. No. 4,551,490 which discloses medicinal grade pressure-sensitive compositions containing polyisobutylenes or blends of polyisobutylenes and butyl rubber, a styrenic radical or block type copolymer, mineral oil and water soluble hydrocolloid gum and a tackifier. Such hydrocolloid containing PSAs have the advantage of providing the desired adhesion to skin and, at the same time, are capable of absorbing transepidermal water loss (i.e., perspiration) or other body fluids, including wound exudates.
Hydrocolloid containing PSAs have found u se in medical applications such as ostomy devices and wound dressings, where the adhesives maintain the device on skin for several days without skin damage. However, existing hydrocolloid PSAs have certain limitations in that they are opaque, lack quick initial tack, and tend to disintegrate upon excessive water absorption. Furthermore, hydrocolloid PSAs are not flexible and/or easily conformable or repositionable on the skin. In addition, they often leave an undesirable residue on the skin.
Polyurethanes are polymeric products of diols or polyols and diisocyanates or polyisocyanates. Despite the broad applications of polyurethane chemistry, polyurethane based PSAs are not widely used and to date have been found suitable for only a few specialized applications. A suitable balance of elastic and viscous properties which is required in a PSA has not been readily attainable in conventional polyurethane materials.
Existing polyurethane based adhesives function either as weak elastomers or simply as high viscosity liquids. The adhesives composed of the elastic type polyurethanes tend to fail by gradually peeling away from surfaces to which they have been applied. The high viscosity type polyurethanes, which are typically obtained by using a substantial excess of polyol, leave a residue upon removal, and their cohesive strength is too low to withstand the stresses applied in many applications.
The difficulty of attaining this balance of viscoelastic characteristics in a polyurethane explains the limited effective use of polyurethane PSA for medical devices applied to the skin.
For example, Rolf Dahl et al., U.S. Pat. No. 3,437,622 discloses a pressure-sensitive adhesive employing a polyurethane polymer in which the isocyanate to hydroxyl group ratio is within a specified range and in which the process employs the addition of tackifiers and plasticizers. Leonard A. Tushaus, U.S. Pat. No. 3,767,040 discloses a pressure-sensitive polyurethane adhesive which has a molecular weight between crosslinks of about 6,000 to 40,000 and a urethane group concentration of about 0.7 to 1.3 per 1,000 grams of polymer. Heinz Muller et al., U.S. Pat. No. 3,930,102 discloses a self-adhesive web having a polyurethane-based adhesive thereon which is produced from a branched polyether and an aliphatic diisocyanate. Dominic Simone, U.S. Pat. No. 4,332,927 discloses the reaction of at least one NCO-terminated prepolymer and at least one polyol in the presence of a dialkyltin dicarboxylated catalyst. Dietmar Schapel, U.S. Pat. No. 4,404,296 and Hans-Heribert Burgdorfer et al., U.S. Pat. No. 4,456,642 disclose a polyol gel made from 15 to 62 weight percent of a high molecular weight covalently cross-linked polyurethane matrix and 85 to 38 weight percent of a liquid dispersing agent which is firmly bonded to the matrix. The liquid dispersing agent is a polyhydroxyl compound having a molecular weight of between 1,000 and 12,000 and an OH number between 20 and 112.
Allen et al., U.S. Pat. No. 4,497,914 discloses an ostomy gasket adhesive comprised of a polyurethane prepared by reaction of an organic polyisocyanate with one or more di or polyfunctional hydroxyl compounds.
Miklos von Bittera et al., U.S. Pat. No. 4,661,099 discloses an adhesive polyurethane gel material which is formed by immobilizing a high molecular weight polymeric polyol in a matrix of a covalently cross-linked polyurethane. Fritz Hostettler, U.S. Pat. No. 4,722,946 discloses a polyurethane formed by the reaction of a mixture of linear and branched polyols, a polyisocyanate and optionally a blowing agent at an isocyanate index of from about 65 to 85.
Francis E. Gould et al., U.S. Pat. No. 5,000,955 discloses a thermally reversible polyurethane hydrogel produced by reacting under anhydrous conditions a non-aromatic organic diisocyanate, with a glycol component in an NCO/OH mole weight ratio of from about 0.900 to 0.980:1. Robert B. Orr, U.S. Pat. No. 5,157,101 discloses a pressure-sensitive polyurethane based adhesive including an isocyanate reactant and an active hydrogen reactant. Dietmar Schapel et al., U.S. Pat. No. 5,362,834 discloses gel compounds based on reaction products of polyols and polyisocyanates in which different polyol components are used, one being one or more polyols having a hydroxyl value below 112 and the other being one or more polyols having hydroxyl values of from 112 to 600.
Despite these efforts, commercially acceptable pressure-sensitive polyurethane adhesives for use particularly with medical devices which attach to the patients' skin such as wound dressings and ostomy appliances have not been successful. While polyurethane based adhesives generally are less irritating to the skin than acrylic based adhesives and have better strength, polyurethane based adhesives remain problematical. This is because it has heretofore been difficult to provide a polyurethane based adhesive which exhibits excellent adhesion over an extended period of time (e.g. 5 days) while maintaining a high degree of cohesive strength so that the medical device can withstand the riggers of 5 day wear.
It would therefore be a significant advance in the art of medical devices applied to the skin to provide an adhesive composition which exhibits excellent adhesion and excellent cohesive strength over extended periods of wear without irritating the patients' skin.